Java StringBuilder ensureCapacity()方法

java.lang.StringBuilder.ensureCapacity() 方法确保了容量至少等于指定的最小值。如果当前容量小于参数，那么一个新的内部数组分配容量更大。新的容量较大：

• minimumCapacity参数。
• 旧容量的两倍，再加上2。

如果 minimumCapacity 参数为非正数，则此方法不执行任何操作，只是返回。

1 语法

public void ensureCapacity(int minimumCapacity)

2 参数

minimumCapacity ： 这是最低所需容量。

3 返回值

此方法不返回任何值。

4 示例 

package com.yiidian;

/**
 * 一点教程网： http://www.yiidian.com
 */
/**
 * Java StringBuilder ensureCapacity()方法
 */
import java.lang.*;

public class StringBuilderDemo {

  public static void main(String[] args) {
  
    StringBuilder str1 = new StringBuilder("tuts point");
    System.out.println("string1 = " + str1);

    // returns the current capacity of the string Builder 1
    System.out.println("Old Capacity = " + str1.capacity());
    /* increases the capacity, as needed, to the specified amount in the 
    given StringBuilder object */
    // returns twice the capacity plus 2
    str1.ensureCapacity(28);
    System.out.println("New Capacity = " + str1.capacity());

    StringBuilder str2 = new StringBuilder("compile online");
    System.out.println("string2 = " + str2);
    // returns the current capacity of string Builder 2
    System.out.println("Old Capacity = " + str2.capacity());
    /* returns the old capacity as the capacity ensured is less than the
    old capacity */
    str2.ensureCapacity(29);
    System.out.println("New Capacity = " + str2.capacity());
  }
} 

输出结果为：

string1 = tuts point
Old Capacity = 26
New Capacity = 54
string2 = compile online
Old Capacity = 30
New Capacity = 30