我如何删除最后一个"

Question

我有一个主类，该类将输出打印到控制台。。。

例如，如果行中包含A和B，我需要打印“Apple”

我将在主方法中通过首先实例化该类的对象来实现这一点，即。

VeggiesAndFruits myVeg1 = new VeggiesAndFruits(AB);
VeggiesAndFruits myVeg2 = new VeggiesAndFruits(A);
System.out.println(myVeg1.getDescription());
System.out.println(myVeg2.getDescription());

代码示例：

public class VeggiesAndFruits
{
String line;

public VeggiesAndFruits(String line)
{
this.line = line;
}

public String getDescription()
    {
        String description = "";

        if(line.contains("A"))
        {
            description += "Apple & ";
        }
        if(line.contains("B"))
        {
            description += "Banana & ";
        }
        if(line.contains("C"))
        {
            description += "Carrot & ";

        return description;
}
}

Answer 1

您可以尝试在字符串上使用int lastIndexOf（int ch）方法。

例如：

int index=description.lastIndexOf('&');

然后可以使用此索引从主字符串中提取一个子字符串，以删除最后一个

String newDescription = description.substring(0, index);

Answer 2

在Java8中，使用StringJoiner：

public String getDescription() {
    StringJoiner description = new StringJoiner(" & ");
    if (line.contains("A"))
        description.add("Apple");
    if (line.contains("B"))
        description.add("Banana");
    if (line.contains("C"))
        description.add("Carrot");
    return description.toString();
}

在Java 5中，使用StringBuilder和if语句：

public String getDescription() {
    StringBuilder description = new StringBuilder();
    if (line.contains("A")) {
        description.append("Apple");
    }
    if (line.contains("B")) {
        if (description.length() != 0)
            description.append(" & ");
        description.append("Banana");
    }
    if (line.contains("C")) {
        if (description.length() != 0)
            description.append(" & ");
        description.append("Carrot");
    }
    return description.toString();
}

或者，正如kaya3所指出的：

public String getDescription() {
    StringBuilder description = new StringBuilder();
    String sep = "";
    if (line.contains("A")) {
        description.append(sep).append("Apple");
        sep = " & ";
    }
    if (line.contains("B")) {
        description.append(sep).append("Banana");
        sep = " & ";
    }
    if (line.contains("C")) {
        description.append(sep).append("Carrot");
        sep = " & ";
    }
    return description.toString();
}

或者问题代码试图做到这一点的方式：

public String getDescription() {
    StringBuilder description = new StringBuilder();
    if (line.contains("A"))
        description.append("Apple & ");
    if (line.contains("B"))
        description.append("Banana & ");
    if (line.contains("C"))
        description.append("Carrot & ");
    if (description.length() != 0)
        description.setLength(description.length() - 3); // remove final " & "
    return description.toString();
}

测验

System.out.println(new VeggiesAndFruits("").getDescription());
System.out.println(new VeggiesAndFruits("A").getDescription());
System.out.println(new VeggiesAndFruits("B").getDescription());
System.out.println(new VeggiesAndFruits("C").getDescription());
System.out.println(new VeggiesAndFruits("AB").getDescription());
System.out.println(new VeggiesAndFruits("AC").getDescription());
System.out.println(new VeggiesAndFruits("BC").getDescription());
System.out.println(new VeggiesAndFruits("CBA").getDescription());

输出（以上所有4种解决方案相同）

Apple
Banana
Carrot
Apple & Banana
Apple & Carrot
Banana & Carrot
Apple & Banana & Carrot

Answer 3

如果使用Java8，我建议在这里使用StringJoiner。正如Javadoc所说，StringJoiner用于构造由分隔符分隔的字符序列。喜欢

public String getDescription() {
    StringJoiner sj = new StringJoiner(" & ");

    if (line.contains("A")) {
        sj.add("Apple");
    }
    if (line.contains("B")) {
        sj.add("Banana");
    }
    if (line.contains("C")) {
        sj.add("Carrot");
    }
    return sj.toString();
}

在早期版本的Java（5）中，可以使用StringBuilder（以及kaya3提到的“胶水”）。

public String getDescription() {
    StringBuilder sb = new StringBuilder();
    String glue = "";
    if (line.contains("A")) {
        sb.append("Apple");
        glue = " & ";
    }
    if (line.contains("B")) {
        sb.append(glue);
        sb.append("Banana");
        glue = " & ";
    }
    if (line.contains("C")) {
        sb.append(glue);
        sb.append("Carrot");
    }
    return sb.toString();
}

在Java5之前，您可以使用StringBuffer

public String getDescription() {
    StringBuffer sb = new StringBuffer();
    String glue = "";
    if (line.contains("A")) {
        sb.append("Apple");
        glue = " & ";
    }
    if (line.contains("B")) {
        sb.append(glue);
        sb.append("Banana");
        glue = " & ";
    }
    if (line.contains("C")) {
        sb.append(glue);
        sb.append("Carrot");
    }
    return sb.toString();
}