String

String类的几个常用的方法的源代码
1、判断String是否为空的方法：isEmpty()

public boolean isEmpty() {
        return value.length == 0;
    }

2、返回String中的某一个字符方法：charAt(int Index)

public char charAt(int index) {
        if((index < 0)||(index>value.length)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return value[index];

    }

3、返回String类的子字符串的方法：substring(int beginIndex, int endIndex)

public String substring(int beginIndex,int endIndex) {
        if(beginIndex < 0) {
            throw new StringIndexOutOfBoundsException(beginIndex);
        }
        if(endIndex > value.length) {
            throw new StringIndexOutOfBoundsException(endIndex);
        }
        int subLen = beginIndex -endIndex;
        if(subLen < 0) {
            throw new StringIndexOutOfBoundsException(subLen);
        }
        return ((beginIndex == 0)&&(endIndex == value.length))? this:new String(value,beginIndex,subLen);
    }

4、比较两个字符串的方法equals(Object anObject)

public boolean equals(Objet anObject) {
        if(this == anObject) {
            return true;
        }
        if(anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            if(n == anotherString.value.length) {
                char[] v1 = value;
                char[] v2 = anotherString.value;
                int i = 0;
                while(n-- != 0) {
                    if(v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }

总的代码

public final class String implements java.io.Serializable,Comparable<String>,CharSequence{
    private final char value[];//定义了一个value[]数组
    private int hash;//定义哈希值
    public String(String original) {//构造函数进行初始化
        this.value = original.value;
        this.hash = original.hash;
    }
    public boolean isEmpty() {//判断String数组是否为空
        return value.length == 0;
    }
    public char charAt(int index) {//返回数组的其中一个元素
        if((index < 0)||(index>value.length)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return value[index];

    }
    public String substring(int beginIndex,int endIndex) {
        if(beginIndex < 0) {
            throw new StringIndexOutOfBoundsException(beginIndex);
        }
        if(endIndex > value.length) {
            throw new StringIndexOutOfBoundsException(endIndex);
        }
        int subLen = beginIndex -endIndex;
        if(subLen < 0) {
            throw new StringIndexOutOfBoundsException(subLen);
        }
        return ((beginIndex == 0)&&(endIndex == value.length))? this:new String(value,beginIndex,subLen);
    }
    public boolean equals(Objet anObject) {
        if(this == anObject) {
            return true;
        }
        if(anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            if(n == anotherString.value.length) {
                char[] v1 = value;
                char[] v2 = anotherString.value;
                int i = 0;
                while(n-- != 0) {
                    if(v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }
}