java - 如何将 BigDecimal 正确显示为字符串

Question

我正在尝试学习java以进入android编程
对于我的实践我正在尝试编写一个具有基本算术运算和小数点按钮的计算器程序
我尝试使用原始数字类型（例如int和double）来完成它，但是如果我使用作为变量类型的双倍，诸如 2.111 之类的数字显示为 2.11099999，但除此之外它似乎工作正常（我的问题在这里给出）
正如我的另一个问题的答案中所建议的那样，我修改了我的程序以使用 BigDecimal数据类型而不是双精度，但是现在当我单击 1 按钮时，尾数显示为 1.0，而不是像以前使用双精度的程序中那样仅显示为 1
我该如何解决这个问题？

更新尾数的代码：

public void updateMantissa(){

    // mantissa_valueBD = BigDecimal.valueOf(mantissa_value);

    if(mantissa_value == BigDecimal.ZERO){
        mantissa_str = "0";
    }
    /*
    else if(ceil(mantissa_value) == mantissa_value){
        mantissa_str = String.valueOf(mantissa_valueBD);
        mantissa_str = mantissa_str.substring(0, mantissa_str.length() - 2 ); 
    }

    else{
        mantissa_str = String.valueOf(mantissa_valueBD);
        mantissa_str = mantissa_str.substring(0, Math.min(mantissa_str.length(), 10));
    }
    */

    // /*
    else if(mantissa_value.setScale(0, RoundingMode.CEILING)== mantissa_value){
        // mantissa_str = String.valueOf(mantissa_value);
        mantissa_str = mantissa_value.toString();
        mantissa_str = mantissa_str.substring(0, mantissa_str.length() - 4 ); 
    }

    else{
        mantissa_str = String.valueOf(mantissa_value);
        mantissa_str = mantissa_str.substring(0, Math.min(mantissa_str.length(), 10));
    }
    // */
    TextView thisText = (TextView) findViewById(R.id.mantissa);
    thisText.setText(mantissa_str);
}

完整代码（MainActivity 类）：

package com.example.calculator;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.TextView;
import static java.lang.Math.pow;
// import static java.lang.Math.ceil;
import java.math.BigDecimal;
import java.math.RoundingMode;

public class MainActivity extends Activity {
// private double mantissa_value = 0;
// private BigDecimal mantissa_value = new BigDecimal(0);
// private BigDecimal opr1BD, opr2BD, resBD, mantissa_valueBD;
/*
private double opr1 = 0;
private double opr2 = 0;
private double res = 0;
// */

BigDecimal opr1 = BigDecimal.ZERO;
BigDecimal opr2 = BigDecimal.ZERO;
BigDecimal res = BigDecimal.ZERO;
BigDecimal tempBD = BigDecimal.ZERO;
BigDecimal mantissa_value = BigDecimal.ZERO;

private enum OprTypes {NONE, PLUS, MINUS, MULT, DIV}
OprTypes oprLatest = OprTypes.NONE;
private boolean oprPlusClicked = false;
private boolean oprMinusClicked = false;
private boolean oprMultClicked = false;
private boolean oprDivClicked = false;
private boolean decimalClicked = false;
private int numOfClicksAfterDecimal = 0;
private String mantissa_str;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    updateMantissa();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

public void updateMantissa(){

    // mantissa_valueBD = BigDecimal.valueOf(mantissa_value);

    if(mantissa_value == BigDecimal.ZERO){
        mantissa_str = "0";
    }
    /*
    else if(ceil(mantissa_value) == mantissa_value){
        mantissa_str = String.valueOf(mantissa_valueBD);
        mantissa_str = mantissa_str.substring(0, mantissa_str.length() - 2 ); 
    }

    else{
        mantissa_str = String.valueOf(mantissa_valueBD);
        mantissa_str = mantissa_str.substring(0, Math.min(mantissa_str.length(), 10));
    }
    */

    // /*
    else if(mantissa_value.setScale(0, RoundingMode.CEILING)== mantissa_value){
        // mantissa_str = String.valueOf(mantissa_value);
        mantissa_str = mantissa_value.toString();
        mantissa_str = mantissa_str.substring(0, mantissa_str.length() - 4 ); 
    }

    else{
        mantissa_str = String.valueOf(mantissa_value);
        mantissa_str = mantissa_str.substring(0, Math.min(mantissa_str.length(), 10));
    }
    // */
    TextView thisText = (TextView) findViewById(R.id.mantissa);
    thisText.setText(mantissa_str);
}

public void onClkBn0(View view){
    TextView thisText = (TextView) findViewById(R.id.mantissa);
    if(decimalClicked == false){
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = mantissa_value.add(BigDecimal.valueOf(0.0));
        updateMantissa();
    }
    else{
        if(mantissa_value == BigDecimal.ZERO){
            if(numOfClicksAfterDecimal == 1){
                mantissa_str = mantissa_str + ".0";
            }
            else{
                mantissa_str = mantissa_str + "0";
            }
        }

        else if(mantissa_value.setScale(0, RoundingMode.CEILING)== mantissa_value){
            if(numOfClicksAfterDecimal == 1){
                mantissa_str = mantissa_str + ".0";
            }
            else{
                mantissa_str = mantissa_str + "0";
            }
        }

        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*0;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*0);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
        thisText.setText(mantissa_str);
    }
}

public void onClkBn1(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+1;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(1.0));
    }

    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*1;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*1);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBn2(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+2;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(2.0));
    }
    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*2;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*2);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBn3(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+3;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(3.0));
    }
    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*3;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*3);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBn4(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+4;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(4.0));
    }
    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*4;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*4);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBn5(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+5;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(5.0));
    }
    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*5;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*5);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBn6(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+6;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(6.0));
    }
    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*6;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*6);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBn7(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+7;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(7.0));
    }
    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*7;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*7);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBn8(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+8;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(8.0));
    }
    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*8;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*8);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBn9(View view){
    if(decimalClicked == false){
        // mantissa_value = mantissa_value*10+9;
        tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0));
        mantissa_value = tempBD.add(BigDecimal.valueOf(9.0));
    }
    else{
        // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*9;
        tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*9);
        mantissa_value = mantissa_value.add(tempBD);
        numOfClicksAfterDecimal++;
    }
    updateMantissa();
}

public void onClkBnDot(View view){
    decimalClicked = true;
}

public void onClkBnCan(View view){
    mantissa_value = BigDecimal.ZERO;
    opr1 = BigDecimal.ZERO;
    opr2 = BigDecimal.ZERO;
    res = BigDecimal.ZERO;
    /*
    opr1 = 0;
    opr2 = 0;
    res = 0;
    // */
    oprLatest = OprTypes.NONE;
    oprPlusClicked = false;
    oprMinusClicked = false;
    oprMultClicked = false;
    oprDivClicked = false;
    decimalClicked = false;
    numOfClicksAfterDecimal = 1;
}


public void onClkBnPlus(View view){
    if(oprPlusClicked == false){
        oprPlusClicked = true;
        opr1 = mantissa_value;
        // mantissa_value = 0;
        mantissa_value = BigDecimal.ZERO;
    }
    else{
        // this should mean opr1 already has some value in it
        // so add the current mantissa value to opr1
        // opr1 = opr1 + mantissa_value;
        opr1 = opr1.add(mantissa_value);
        mantissa_value = BigDecimal.ZERO;
    }
    oprLatest = OprTypes.PLUS;
}


public void onClkBnMinus(View view){
    if(oprMinusClicked == false){
        oprMinusClicked = true;
        opr1 = mantissa_value;
        mantissa_value = BigDecimal.ZERO;
    }
    else{
        // this should mean opr1 already has some value in it
        // so add the current mantissa value to opr1
        // opr1 = opr1 - mantissa_value;
        opr1 = opr1.subtract(mantissa_value);
        mantissa_value = BigDecimal.ZERO;
    }
    oprLatest = OprTypes.MINUS;
}

public void onClkBnMult(View view){
    if(oprMultClicked == false){
        oprMultClicked = true;
        opr1 = mantissa_value;
        mantissa_value = BigDecimal.ZERO;
    }
    else{
        // this should mean opr1 already has some value in it
        // so add the current mantissa value to opr1
        // opr1 = opr1 * mantissa_value;
        opr1 = opr1.multiply(mantissa_value);
        mantissa_value = BigDecimal.ZERO;
    }
    oprLatest = OprTypes.MULT;
}

public void onClkBnDiv(View view){
    if(oprDivClicked == false){
        oprDivClicked = true;
        opr1 = mantissa_value;
        mantissa_value = BigDecimal.ZERO;
    }
    else{
        // this should mean opr1 already has some value in it
        // so add the current mantissa value to opr1
        // opr1 = opr1 / mantissa_value;
        opr1 = opr1.divide(mantissa_value);
        mantissa_value = BigDecimal.ZERO;
    }
    oprLatest = OprTypes.DIV;
}


public void onClkBnRes(View view){
    if(oprPlusClicked == true || oprMinusClicked == true || oprMultClicked == true || oprDivClicked == true){
        switch(oprLatest){
        case PLUS:
            // mantissa_value = opr1 + mantissa_value;
            mantissa_value = opr1.add(mantissa_value);
            break;
        case MINUS:
            // mantissa_value = opr1 - mantissa_value;
            mantissa_value = opr1.subtract(mantissa_value);
            break;
        case MULT:
            // mantissa_value = opr1 * mantissa_value;
            mantissa_value = opr1.multiply(mantissa_value);
            break;
        case DIV:
            // mantissa_value = opr1 / mantissa_value;
            mantissa_value = opr1.divide(mantissa_value);
            break;
        case NONE:
            break;
        }
    }
    oprLatest = OprTypes.NONE;
    oprPlusClicked = false;
    oprMinusClicked = false;
    oprMultClicked = false;
    oprDivClicked = false;
    updateMantissa();
}
 }

------ 编辑 ------
如果我做这样的事情，

public static void main(String[] args){
    // double a;
    a = 2.111;
    System.out.println(a);
}

它正好显示 2.111 而不是 2.1109999。这是为什么？

------ 编辑 2 ------

我已经对我的程序的逻辑进行了更改，因此它现在可以在字符串上执行与显示相关的任何操作，同时使用 Double.parseDouble() 函数将尾数字符串值转换为 double 以执行与计算相关的任何操作。如果有人想评论它，下面给出了更新的代码

package com.example.calculator;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.TextView;
import static java.lang.Math.pow;
import static java.lang.Math.ceil;
// import java.math.BigDecimal;
import java.text.NumberFormat;

public class MainActivity extends Activity {

     private double mantissa_value = 0;
    // private BigDecimal mantissa_value = new BigDecimal(0);
    // private BigDecimal opr1BD, opr2BD, resBD, mantissa_valueBD;
    // /*
    private double opr1 = 0;
    // */
    NumberFormat number =  NumberFormat.getNumberInstance();

    private enum OprTypes {NONE, PLUS, MINUS, MULT, DIV}
    OprTypes oprLatest = OprTypes.NONE;
    private boolean oprPlusClicked = false;
    private boolean oprMinusClicked = false;
    private boolean oprMultClicked = false;
    private boolean oprDivClicked = false;
    private boolean decimalClicked = false;
    private boolean resetMantissa = true;
    private String mantissa_str;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // updateMantissa();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    public void updateMantissa(){
        // This is the version that should get called from the num pad buttons, 0 - 9
        updateMantissa(true);
    }
    public void updateMantissa(boolean frmNumPad){
        // this is the version that should get called from other buttons besides the num pad buttons
        if(frmNumPad != true){
            long mantissa_val_int_part = (long)mantissa_value;
            if(mantissa_value == (double)mantissa_val_int_part){
                mantissa_str = mantissa_str.substring(0, mantissa_str.length() - 2 );
            }
            else if (mantissa_str.length() > 10){
                mantissa_str = mantissa_str.substring(0, Math.min(mantissa_str.length(), 10));
            }

        }


        TextView thisText = (TextView) findViewById(R.id.mantissa);
        thisText.setText(mantissa_str);
    }

    public void onClkBn0(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }

        if(decimalClicked == false){
            if( !(Double.parseDouble(mantissa_str)==0.0) ) 
                mantissa_str = mantissa_str + "0";
        }
        else{
            mantissa_str = mantissa_str + "0";
        }
        TextView thisText = (TextView) findViewById(R.id.mantissa);
        thisText.setText(mantissa_str);
    }

    public void onClkBn1(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "1";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBn2(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "2";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBn3(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "3";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBn4(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "4";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBn5(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "5";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBn6(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "6";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBn7(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "7";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBn8(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "8";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBn9(View view){
        if (resetMantissa == true){
            mantissa_str = "";
            resetMantissa = false;
        }
        mantissa_str = mantissa_str + "9";
        mantissa_value = Double.parseDouble(mantissa_str);
        updateMantissa();
    }

    public void onClkBnDot(View view){
        if(decimalClicked == false){
            decimalClicked = true;
            mantissa_str = mantissa_str + ".";
        }
    }

    public void onClkBnCan(View view){
        mantissa_value = 0;
        // /*
        opr1 = 0;
        // */
        oprLatest = OprTypes.NONE;
        oprPlusClicked = false;
        oprMinusClicked = false;
        oprMultClicked = false;
        oprDivClicked = false;
        decimalClicked = false;
        mantissa_value = 0;
        opr1 = 0;
        resetMantissa = true;
        updateMantissa(false);
    }


    public void onClkBnPlus(View view){
        if(oprPlusClicked == false){
            oprPlusClicked = true;
            decimalClicked = false;
            opr1 = Double.parseDouble(mantissa_str);
            mantissa_value = 0;
        }
        else{
            // this should mean opr1 already has some value in it
            // so add the current mantissa value to opr1
            mantissa_value = Double.parseDouble(mantissa_str);
            opr1 = opr1 + mantissa_value;
            mantissa_value = opr1;
            decimalClicked = false;
            mantissa_str = Double.toString(mantissa_value);
            updateMantissa(false);
        }
        oprLatest = OprTypes.PLUS;
        resetMantissa = true;
    }


    public void onClkBnMinus(View view){
        if(oprMinusClicked == false){
            oprMinusClicked = true;
            decimalClicked = false;
            opr1 = Double.parseDouble(mantissa_str);
            mantissa_value = 0;
        }
        else{
            // this should mean opr1 already has some value in it
            // so add the current mantissa value to opr1
            mantissa_value = Double.parseDouble(mantissa_str);
            opr1 = opr1 - mantissa_value;
            mantissa_value = opr1;
            decimalClicked = false;
            mantissa_str = Double.toString(mantissa_value);
            updateMantissa(false);
        }
        oprLatest = OprTypes.MINUS;
        resetMantissa = true;
    }

    public void onClkBnMult(View view){
        if(oprMultClicked == false){
            oprMultClicked = true;
            decimalClicked = false;
            opr1 = Double.parseDouble(mantissa_str);
            mantissa_value = 0;
        }
        else{
            // this should mean opr1 already has some value in it
            // so add the current mantissa value to opr1
            mantissa_value = Double.parseDouble(mantissa_str);
            opr1 = opr1 * mantissa_value;
            mantissa_value = opr1;
            decimalClicked = false;
            mantissa_str = Double.toString(mantissa_value);
            updateMantissa(false);
        }
        oprLatest = OprTypes.MULT;
        resetMantissa = true;
    }

    public void onClkBnDiv(View view){
        if(oprDivClicked == false){
            oprDivClicked = true;
            decimalClicked = false;
            opr1 = Double.parseDouble(mantissa_str);
            mantissa_value = 0;
        }
        else{
            // this should mean opr1 already has some value in it
            // so add the current mantissa value to opr1
            mantissa_value = Double.parseDouble(mantissa_str);
            opr1 = opr1 / mantissa_value;
            mantissa_value = opr1;
            decimalClicked = false;
            mantissa_str = Double.toString(mantissa_value);
            updateMantissa(false);
        }
        oprLatest = OprTypes.DIV;
        resetMantissa = true;
    }


    public void onClkBnRes(View view){
        mantissa_value = Double.parseDouble(mantissa_str);
        if(oprPlusClicked == true || oprMinusClicked == true || oprMultClicked == true || oprDivClicked == true){
            switch(oprLatest){
            case PLUS:
                mantissa_value = opr1 + mantissa_value;
                break;
            case MINUS:
                mantissa_value = opr1 - mantissa_value;
                break;
            case MULT:
                mantissa_value = opr1 * mantissa_value;
                break;
            case DIV:
                mantissa_value = opr1 / mantissa_value;
                break;
            case NONE:
                break;
            }
        }
        oprLatest = OprTypes.NONE;
        oprPlusClicked = false;
        oprMinusClicked = false;
        oprMultClicked = false;
        oprDivClicked = false;
        decimalClicked = false;
        mantissa_str = Double.toString(mantissa_value);
        updateMantissa(false);
    }

    public void onClkBnOff(View view){
        finish();
    }

}

score 1 · Accepted Answer

基本上它仅以这种方式显示 Double 。在显示数字之前添加以下小代码应该会有所帮助。

BigDecimal chk=BigDecimal.valueOf(val);
BigDecimal chk3=chk.subtract(BigDecimal.valueOf(chk.intValue()));
if(chk3.compareTo(BigDecimal.ZERO)==0)
    System.out.print(BigDecimal.valueOf(chk.intValue()));
else
    System.out.print(chk);

chk是您要显示的值。只需添加chk3这就是它的int价值。此代码打印50.1for50.1和50for 50.00。希望这可以帮助。

- 编辑 -

我在您的代码中发现了另一个错误。你正在做：

tempBD = mantissa_value.multiply(BigDecimal.valueOf(10.0)); 这是错误的，因为存储了最接近 10.0 的值，但您想要 10.0，那么您应该这样做：

tempBD = mantissa_value.multiply(BigDecimal.valueOf("10.0"));

因此 void 的修改代码onClkBn1(View view)如下：

public void onClkBn1(View view){
if(decimalClicked == false){
    // mantissa_value = mantissa_value*10+1;
    tempBD = mantissa_value.multiply(BigDecimal.valueOf("10.0"));
    mantissa_value = tempBD.add(BigDecimal.valueOf("1.0"));
}

else{
    // mantissa_value = mantissa_value + pow(10, -numOfClicksAfterDecimal)*1;
    tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*1);
    mantissa_value = mantissa_value.add(tempBD);
    numOfClicksAfterDecimal++;
}
updateMantissa();
}

而且我不确定您不tempBD = BigDecimal.valueOf(pow(10, -numOfClicksAfterDecimal)*1);应该如何使用它Math.pow(double, double)。所以请检查一下。

score 1 · Accepted Answer

通过阅读您链接到的问题，尚不清楚您关注的是浮动精度问题还是浮动打印问题。原始问题中的人们建议使用 BigDecimal，但我觉得您最初的担忧与后者有关 - 即打印值 - 这就是您仍然面临的问题。

使用打印双精度值几乎不是一个好主意String.valueOf()。幕后发生的事情是根据您的默认语言环境将浮点值转换为字符串。您应该自己执行转换，而不是离开系统进行转换。

做到这一点的方法是DecimalFormat课堂。示例代码：

double mantissa_value = 2.11099999;

DecimalFormat df = new DecimalFormat("0.###");
// Un-comment the line below to take English locale into account when converting
//df.setDecimalFormatSymbols(new DecimalFormatSymbols(Locale.ENGLISH));

// will print '2.11099999' this is what you get in your original case
System.out.println( String.valueOf(mantissa_value) ); 

// will print '2.111' or '2,111' depending on your locale. if you uncomment the line above for English locale it will print '2.111'
System.out.println( df.format(mantissa_value) );

上述十进制格式将打印小数点后 1、2 或 3 位的双精度值。如果您需要可变精度，您可以在用户输入字符时将计数器保留在变量中，然后使用该计数器生成DecimalFormat所需的十进制数字。对于这种情况，可以采用相同的方法BigDecimal。我希望这会有所帮助

java - 如何将 BigDecimal 正确显示为字符串

2 回答 2

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